1. Field of the Invention
The invention pertains to the field of electronic displays. More particularly, the invention pertains to using wire electrodes in fibers, tubes and electroded sheets, to build the structure in a flat panel display.
2. Description of Related Art
Within the electronic display space there is a group of displays that create an image by modulating an electro-optic material. An electro-optic material is defined as a material that changes state in an electric field. Some of these materials can be passively addressed or simply addressed by sandwiching the electro-optic material between two orthogonal arrays of electrodes. However, this passive addressing scheme requires that the electro-optic material has a threshold or its optical properties have an abrupt change over a small change in applied voltage. Most liquid crystal (LC) materials have a steep enough threshold that allows them to be passively addressed. If the electro-optic material does not have a voltage threshold or its threshold is not steep enough (the voltage to totally modulate the material has to be less than twice the voltage of where the materials electro-optic properties start to change), then the electro-optic material has to be actively addressed. Active addressing means that a switch, like a transistor, that has a voltage threshold is used to place the voltage across the electro-optic material. Other active addressing switches that have been used are diodes, plasmas, and micro-electro-mechanical systems (MEMS). Active addressing is also used in cases that require video rate images because passive addressing requires that a line at a time addressing scheme is used and therefore the speed to update the image is limited to the number of lines in the display times the minimum response time of the electro-optic media.
There are several different types of electro-optic materials. The most well known and widely used electro-optic materials are liquid crystal molecules. In the liquid crystal family, a vast range of molecules could potentially be used to create the electro-optic modulated material. Some of these liquid crystal molecules include, but are not limited to, twisted nematic, cholesteric-nematic, dichroic dye (or guest-host), dynamic scattering mode, smectic, and polymer dispersed. Most of these liquid crystal molecules require other films, such as alignment layers, polarizers, and reflective films.
Another type of electro-optic material is electrophoretic. Electrophoretic material is a suspension of small charged particles in a liquid solution. If the particles have a similar density as the liquid solution, they are not affected by gravity. Therefore the only way to move the particles is using an electric field. By applying a voltage potential across the electrophoretic solution, the charged particles are forced to move in the suspension to one of the contacts. The opposite charge moves the particles in the other direction. The electrophoretic suspension is designed such that the particles are a different color than the liquid solution or there are two different colored particles with opposite charge states.
Another type of electro-optic material is a twisting ball or Gyricon material. It was initially called twisting ball material because it is composed of small bichromal spheres, one side coated black, the other white with opposite charges on the two halves. Therefore, when the twisting ball material is placed in an electric field, the bichromal spheres all rotate to display one optical property of the material and when the opposite voltage is applied, the material displays the other colored state. This Gyricon material can also be made in a cylindrical form.
Research Frontiers Incorporated has developed another electro-optic material that they call a suspended particle device (SPD) which consists of microscopic particles in a liquid suspension. These microscopic particles are elongated in one direction and, when randomly orientated, block light. When a voltage is applied across the electro-optic material, the particles align and transmit light.
Most of these electro-optic materials do not have a voltage threshold and must be actively addressed. Some of the liquid crystal materials use an active transistor back plane to address the displays, but these types of displays are presently limited in size due to the complicated manufacturing process. Transmissive displays using liquid crystal materials and a plasma-addressed back plane have been demonstrated in U.S. Pat. No. 4,896,149, herein incorporated by reference, however, these plasma-addressed back planes are also limited in size due to availability of the thin microsheet to create the plasma cells.
One potential solution for producing large size displays is to use fibers/tubes to create the plasma cells. Using tubes to create a plasma-addressable plasma cell was first disclosed in U.S. Pat. No. 3,964,050, herein incorporated by reference. One potential issue in producing large plasma-addressed tubular displays is creating the top column electrode plate. This plate has to be composed of an array of lines to address that set the charge in the plasma tubes. When addressing a thin electro-optic material like a LC or electrophoretic material, these electrode lines have to be wide enough to spread the charge across the width of the entire pixel. The lines also have to be conductive enough to set the charge in the plasma tube so the display can be addressed at video rates. A traditional patterned indium tin oxide (ITO) transparent conductor works fine for smaller panels where processing the panel is easy and the lines are short, however to address very large panels, the ITO lines are not conductive enough and patterning of the lines becomes very expensive.
One method to solve this problem has been proposed in U.S. patent application Ser. No. 11/236,904 “Electrode Enhancements for Fiber-Based Displays”, filed Sep. 28, 2005, and herein incorporated by reference. In that application, fiber containing an electrode is used to form the column electrode plane. The electrode is composed of a wire electrode, which carries the bulk of the current and a transparent conductive electrode, which is connected to the wire electrode and is used to spread the voltage across the surface of the fiber.
Connecting a higher conductive metal film electrode to a transparent conductive film to spread the voltage of the electrode is also traditionally used in the top electrode plate of a plasma display (PDP). The top PDP plates use a 50 μm wide by about 1 μm thick Cr/Cu/Cr stack to carry current and a thin ITO coating to spread the effect of the voltage, hence spreading the firing of the plasma. These electrode coatings are evaporated or sputtered and then photolithograph is used to pattern them and they are then etched into lines using a wet etch or a reactive ion etch (RIE).
Photovoltaic cells also use conductive metal lines connected to transparent conductive coatings to collect the current from the photovoltaic device. The use of wire connected to a transparent conductive coating has been disclosed by Nanosolar in U.S. Pat. Nos. 6,936,761 and 7,022,910, herein incorporated by reference, for solar cell applications.
Plasma display panels (PDP) have been around for 40 years, however, color PDPs did not receive much attention until the invention of the three electrode surface discharge structure (G. W. Dick, “Three-Electrode per PEL AC Plasma Display Panel”, 1985 International Display Research Conf., pp. 45-50; U.S. Pat. Nos. 4,554,537, 4,728,864, 4,833,463, 5,086,297, 5,661,500, and 5,674,553). The three electrode surface discharge structure, shown in FIG. 1, advances many technical attributes of the display, but its complex manufacturing process and detailed structure makes manufacturing complicated and costly.
Currently, plasma display structures are built up layer by layer on specialty glass substrates using many complex processing steps. FIG. 1 illustrates the basic structure of a surface discharge AC plasma display made using standard technology. The PDP can be broken down into two parts: top plate 10 and bottom plate 20. The top plate 10 has rows of paired electrodes referred to as the sustain electrodes 11a, 11b. The sustain electrodes are composed of wide transparent indium tin oxide (ITO) electrodes 12 and narrow Cr/Cu/Cr bus electrodes 13. These electrodes are formed using sputtering and multi-layer photolithography. The sustain electrodes 11 are covered with a thick (25 μm) dielectric layer 14 so that they are not exposed to the plasma. Silk-screening a high dielectric paste over the surface of the top plate and consolidating it in a high temperature process step forms this dielectric layer 14. A magnesium oxide layer (MgO) 15 is deposited by electron-beam evaporation or sputtering over the dielectric layer to enhance secondary emission of electrons and improve display efficiency. The bottom plate 20 has columns of address electrodes 21 formed by silk-screening silver paste and firing the paste in a high temperature process step. Barrier ribs 22 are then formed between the address electrodes 21. These ribs 22, typically 50 μm wide and 120 μm high, are formed using either a greater than ten layer multiple silk-screening process, embossing a frit paste, or a sandblasting process. In the sandblasting method, barrier rib paste is blade coated on the glass substrate. A photoresist film laminated on the paste is patterned by photolithography. The rib structure is formed by sandblasting the rib paste between the exposed pattern, followed by removal of the photoresist layer and a high temperature consolidation of the barrier rib 22. Alternating red 23R, green 23G, and blue 23B phosphors are silk-screened into the channels between the barrier ribs to provide color for the display. After silk-screening the phosphors 23, the bottom plate is sandblasted to remove excess phosphor in the channels. The top and bottom plates are frit sealed together and the panel is evacuated and backfilled with a gas mixture containing xenon.
The basic operation of the display requires a plasma discharge where the ionized xenon generates ultraviolet (UV) radiation. This UV light is absorbed by the phosphor and emitted as visible light. To address a pixel in the display, an AC voltage is applied across the sustain electrodes 11, which is large enough to sustain a plasma, but not large enough to ignite one. (A plasma is a lot like a transistor, as the voltage is increased nothing happens until a specific voltage is reached where it turns on.) Then an additional short voltage pulse is applied to the address electrode 21, which adds to the sustain voltage and ignites the plasma by adding to the total local electric field, thereby breaking down the gas into a plasma. Once the plasma is formed, electrons are pulled out of the plasma and deposited on the MgO layer 15. These electrons are used to help ignite the plasma in the next phase of the AC sustain electrodes. To turn the pixel off, an opposite voltage must be applied to the address electrode 21 to drain the electrons from the MgO layer 15, thereby leaving no priming charge to ignite the plasma in the next AC voltage cycle on the sustain electrodes. Using these priming electrons, each pixel can be systematically turned on or off. To achieve gray levels in a plasma display, each video frame is divided into 8 bits (256 levels) and, depending on the specific gray level, the pixels are turned on during these times.
An entirely new method of manufacturing plasma displays using complex-shaped fibers containing wire electrodes to build the panel structure in a display solved many of the cost and size issues involved with manufacturing PDPs (C. Moore and R. Schaeffler, “Fiber Plasma Display”, SID '97 Digest, pp. 1055-1058; U.S. Pat. No. 5,984,747 GLASS STRUCTURES FOR INFORMATION DISPLAYS, herein incorporated by reference). The fiber-based method of manufacturing creates plasma displays that look and operate identical to the traditional panel structure, FIG. 1, but the structure in the panel is totally fabricated using complex-shaped glass fibers containing wire electrodes, as shown in FIG. 2.
The entire functionality of the standard plasma display (FIG. 1) is created by replacing the top 16 and bottom 24 plates with respective sheets of top 17 and bottom 27 fibers (FIG. 2) sandwiched between plates (16 and 24) of soda lime glass. Each row of the bottom plate is composed of a single fiber 27 that includes the address electrode 21, barrier ribs 22, plasma channel 25 and the phosphor layers 23. Each column of the top plate is composed of a single fiber 17 that includes two sustain electrodes 11 and a thin built-in dielectric layer 14 over the electrodes 11a and 11b which is covered with a MgO layer 15.
All of the glass fibers are preferably formed using a fiber draw process similar to that used to produce optical fiber in the telecommunications industry. The glass fibers are drawn from a large glass preform, which is formed using hot glass extrusion. Metal wire electrodes are fed through a hole in the glass preform and are co-drawn with the glass fiber. The phosphor layers 23 are subsequently sprayed into the channels 25 of the bottom fiber 27 and a thin MgO coating 15 is applied to the top fiber 17. Sheets of top 17 and bottom fibers 27 are placed between two glass plates (16 and 24). The glass plates are frit sealed together with the wire electrodes extending through the frit seal. The panel is evacuated and backfilled with a xenon-containing gas and the wire electrodes are directly connected to the drive circuitry.
There are several advantages to creating plasma displays using arrays of fibers. The largest advantage is a reduction of over a factor of 2 in the manufacturing costs of the panel with a 10 times less capital cost requirement. These economical advantages result from a manufacturing process with no multi-level alignment process steps, no need for large area vacuum deposition equipment, about ½ the process steps (potentially leading to higher yields), simpler process steps (hot glass extrusion, fiber draw, and phosphor spraying compared to photolithography, precision silk screening, and vacuum deposition processes) and the ability to create many different size displays using the same manufacturing equipment. Although using fibers to create the structure in a display has drastically simplified the manufacturing of the panel leading to a large reduction in manufacturing cost, the initial fiber-based work had no advancements to the performance of the display.
Much advancement in fabricating fiber-based plasma displays have been achieved since the initial invention. Some process improvements in fabricating fiber-based displays are listed in U.S. Pat. Nos. 6,247,987 and 6,354,899, which include fiber, array and panel forming processes. These patents are hereby incorporated herein by reference. Since plasma displays still suffer from low luminous efficiencies and poor bright room contrast there has been a focus on using fibers to help solve some of these issues. U.S. Pat. No. 6,414,433, herein incorporated by reference, is the first indication of controlling the intra-pixel shape to increase the plasma efficiency and U.S. Pat. No. 6,771,234, also incorporated herein by reference, shows methods of increasing the length of the plasma glow to increase the displays efficiency. Adding a color filter to a display increases the bright room contrast because it subtracts out ⅔ of the reflected light (i.e. the red pixel absorbs green and blue). In traditional plasma display panels (PDPs), the concept of adding a color filter was first patented by Pioneer Electronic Corporation in U.S. Pat. No. 5,838,105, herein incorporated by reference. NEC Corporation has been fabricating plasma displays using a color filter contained within the top plate and aligning the color filter with the corresponding phosphor colors in the bottom plate, as described in U.S. Pat. No. 6,072,276, herein incorporated by reference.
One of the best methods of adding a color filter to a fiber-based plasma display is to flip the entire fiber panel upside down, as covered in U.S. Pat. No. 6,570,339, herein incorporated by reference, and shown in FIGS. 3 and 4. In these examples the fibers 47 are composed of a colored glass and are on the side of the display facing the view. The light generated from the color phosphors 23 has to be transmitted through the colored glass fibers 47B, 47G, and 47R, which increases the color purity of the display. Any incident light on the panel will be partially absorbed by the colored fibers 47, hence increasing the bright room contrast. Curved displays up to 360 degrees can be fabricated as covered under U.S. Pat. No. 6,750,605, herein incorporated by reference, because the fibers can be bent and curved glass plates can be used as the vacuum vessel. Adding lenses to the surface of the fibers also allows for the fabrication of multiple view and 3-dimensional display as covered in U.S. Pat. No. 7,082,236, incorporated herein by reference.
Small hollow tubes were first disclosed in 1974 in U.S. Pat. No. 3,602,754 CAPILLARY TUBE GAS DISCHARGE DISPLAY PANELS AND DEVICES assigned to Owens-Illinois and incorporated herein by reference. This patent was followed by U.S. Pat. Nos. 3,654,680, 3,927,342 and 4,038,577, all herein incorporated by reference, which explain methods of creating a plasma display using small glass tubes, as shown in FIG. 5. These patents cover using small glass tubes (T) with conductors (C) applied to the outside surface of the tubes. Although Owens-Illinois had the initial tubular plasma display patents all the initial work on tubular plasma displays was done by Control Data. Control Data focused on using an array of gas filled hollow tubes to produce the rib structure in a plasma display panel (PDP). The electrodes to ignite the plasma inside the tubes were placed on a glass or plastic substrate and the electroded substrates were sandwiched around the gas filled hollow tubes, as shown in FIG. 6. The Control Data work was published by W. Mayer and V. Bonin, “Tubular AC Plasma Panels,” 1972 IEEE Conf. Display Devices, Conf. Rec., New York, pp. 15-18, and R. Storm, “32-Inch Graphic Plasma Display Module,” 1974 SID Int. Symposium, San Diego, pp. 122-123 and included in U.S. Pat. Nos. 3,964,050 and 4,027,188, all herein incorporated by reference. Control Data Corporation also received three US Air Force contracts to develop the tubular plasma display: AD-728623, “Large Screen Plasma Display”, 1971; AD-782383, “Large Area Plasma Display Module”, 1974; and AD-766933, “Plasma Display Color Techniques Using Tubular Construction”, 1973, incorporated herein by reference. In the last U.S. Air Force contract, Control Data focused on adding color phosphors inside the plasma tubes to create a multicolor tubular plasma display. Control Data also discloses depositing a work-function lowering substance inside the discharge tubes.
The only other known group working or having worked on tubular plasma displays is Shinoda's group at Fujitsu in Japan. The first tubular publications or patents from the Fujitsu group were in 2000. Shinoda's group has patented a method of coating a separate setter with a phosphor layer and inserting it into a plasma tube, as discussed U.S. Pat. Nos. 6,577,060, 6,677,704, 6,794,812, 6,836,063, 6,841,929, 6,930,442, 6,932,664, 6,969,292, and 7,049,748, all herein incorporated by reference. Shinoda's group at Fujitsu has also published several papers on tubular plasma display: T. Shinoda et al. “New Approach for Wall Display with Fine Tube Array Technology” SID 2002, pp. 1072-1075; M. Ishimoto et al. “Discharge Observation of Plasma Tubes”, SID 2003 pp. 36-39; H. Hirakawa et al., “Dynamic Driving Characteristics of Plasma Tubes Array”, SID 2004, pp. 810-813; Awanoto et al., “Development of Plasma Tube Array Technology for Extra-Large-Area Displays”, SID 2005, pp. 206-209.
There is a need in the art for a durable, easy to manufacture, low cost method of forming large electronic displays.